1. Technical Field
The present disclosure relates to a base station, a terminal and a communication method used for machine-type communications (MTC).
2. Description of the Related Art
In recent years, machine-type communications (MTC) using a cellular network has been studied (see, for instance, 3GPP TR 36.888 V12.0.0 Machine-Type Communications (MTC) User Equipments (UEs) based on LTE). MTC is expected to have applications to automatic meter inspection, inventory management by a smart meter, physical distribution management utilizing position information, pet and livestock management, and mobile payment. It is assumed that in MTC, an MTC terminal is connected to a network. It is expected that a large amount of MTC terminals is disposed, and yet the amount of traffic of each MTC terminal is not so large. Thus, the MTC terminals preferably have a low cost, and a low power consumption. Also, an MTC terminal may be disposed in the underground of a building where radio waves do not reach easily, enhancement of the coverage is also called for.
For expansion of LTE-Advanced standardized by 3GPP, in order to achieve a low cost of MTC terminal, the following approach is considered: the resources of MTC terminal used for communication are limited to 6 physical resource blocks (PRB) or less regardless of the system bandwidth. When the system bandwidth is wider than 6 PRB, MTC terminal receives a signal in only a portion of the system bandwidth and performs transmission and reception. The PRB used for transmission and reception can be changed by retuning. The resources of 6 PRB or less are called Narrowband. It is stipulated that Narrowband is formed by consecutive PRBs. As the definition of Narrowband, several methods have been proposed, including a method of forming Narrowband by dividing a band into 6 PRB each from one end of the band, and a method of forming Narrowband by dividing a band from the center of the band (see, for instance, R1-153567 “WF on Narrowband Definition for Rel-13 MTC UEs”).
In LTE, a RBG size, which indicates the number of RBs that constitute one resource block group (RBG), is defined according to the number of RBs included in the system bandwidth. The RBG is a resource obtained by dividing the band into a number of consecutive PRBs from one end of the band sequentially, the number is being specified by the RBG size. The RBG size is a parameter used for type 0, type 1 resource allocation for DL. In type 0 resource allocation, resources are allocated in units of RBG. In type 1, each RBG belongs to one of subsets. The number of subsets is the same as the RBG size. In resource allocation, a subset is selected first, and resources are allocated to each of multiple PRBs in each RBG belonging to the selected subset. Like this, RBG is related to the unit of resource allocation of terminals (legacy UE) in related art.
Also, as a method of connecting to a network, an MTC terminal may receive control information stepwise. First, similarly to a terminal in related art, the MTC terminal receives a master information block (MIB). The MIB is placed on 72 carriers (equivalent to 6 PRB) positioned at the center of the system bandwidth, thus an MTC terminal, which performs transmission and reception by Narrowband, can also perform reception by tuning to the central frequency. However, a system information block (SIB) subsequently received by a terminal in related art includes unwanted information for the MTC terminal, and may be transmitted to a broad band. Thus, setting of a SIB for MTC is being studied so that the SIB may be received by the MTC terminal. Thus, the following approach is being studied: the MTC terminal is notified of a transport block size (TBS) of MTC SIB1 using a spare bit prepared in the MIB, and the location of PRB in which MTC SIB1 is placed is determined based an ID called PCID that identifies an cell. The MTC terminal receives MTC SIB1 by retuning to a Narrowband, in which MTC SIB1 is placed, in accordance with the notification of MIB.